@fto-consult/common/src/lib/currency/convert.js

Un ensemble de bibliothèques et d'utilistaires communs pour le développement d'applications javascript

// Copyright 2022 @fto-consult/Boris Fouomene. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Create a safe reference to the money.js object for use below.
var fx = function(obj) {
	return new fxWrapper(obj);
};

/* --- Setup --- */

// fxSetup can be defined before loading money.js, to set the exchange rates and the base
// (and default from/to) currencies - or the rates can be loaded in later if needed.
var fxSetup = root.fxSetup || {
	rates : require("./currencies.json"),
	base : ""
};

// Object containing exchange rates relative to the fx.base currency, eg { "GBP" : "0.64" }
fx.rates = fxSetup.rates;

// Default exchange rate base currency (eg "USD"), which all the exchange rates are relative to
fx.base = fxSetup.base;

// Default from / to currencies for conversion via fx.convert():
fx.settings = {
	from : fxSetup.from || fx.base,
	to : fxSetup.to || fx.base
};


/* --- Conversion --- */

// The base function of the library: converts a value from one currency to another
var convert = fx.convert = function(val, opts) {
	// Convert arrays recursively
	if (typeof val === 'object' && val.length) {
		for (var i = 0; i< val.length; i++ ) {
			val[i] = convert(val[i], opts);
		}
		return val;
	}

	// Make sure we gots some opts
	opts = opts || {};

	// We need to know the `from` and `to` currencies
	if( !opts.from ) opts.from = fx.settings.from;
	if( !opts.to ) opts.to = fx.settings.to;

	// Multiple the value by the exchange rate
	return val * getRate( opts.to, opts.from );
};

// Returns the exchange rate to `target` currency from `base` currency
var getRate = function(to, from) {
	// Save bytes in minified version
	var rates = fx.rates;

	// Make sure the base rate is in the rates object:
	rates[fx.base] = 1;

	// Throw an error if either rate isn't in the rates array
	if ( !rates[to] || !rates[from] ) throw "fx error";

	// If `from` currency === fx.base, return the basic exchange rate for the `to` currency
	if ( from === fx.base ) {
		return rates[to];
	}

	// If `to` currency === fx.base, return the basic inverse rate of the `from` currency
	if ( to === fx.base ) {
		return 1 / rates[from];
	}

	// Otherwise, return the `to` rate multipled by the inverse of the `from` rate to get the
	// relative exchange rate between the two currencies
	return rates[to] * (1 / rates[from]);
};


/* --- OOP wrapper and chaining --- */

// If fx(val) is called as a function, it returns a wrapped object that can be used OO-style
var fxWrapper = function(val) {
	// Experimental: parse strings to pull out currency code and value:
	if ( typeof	val === "string" ) {
		this._v = parseDecimal(val.replace(/[^0-9-.]/g, ""));
		this._fx = val.replace(/([^A-Za-z])/g, "");
	} else {
		this._v = val;
	}
};

// Expose `wrapper.prototype` as `fx.prototype`
var fxProto = fx.prototype = fxWrapper.prototype;

// fx(val).convert(opts) does the same thing as fx.convert(val, opts)
fxProto.convert = function() {
	var args = Array.prototype.slice.call(arguments);
	args.unshift(this._v);
	return convert.apply(fx, args);
};

// fx(val).from(currency) returns a wrapped `fx` where the value has been converted from
// `currency` to the `fx.base` currency. Should be followed by `.to(otherCurrency)`
fxProto.from = function(currency) {
	var wrapped = fx(convert(this._v, {from: currency, to: fx.base}));
	wrapped._fx = fx.base;
	return wrapped;
};

// fx(val).to(currency) returns the value, converted from `fx.base` to `currency`
fxProto.to = function(currency) {
	return convert(this._v, {from: this._fx ? this._fx : fx.settings.from, to: currency});
};


/* --- Module Definition --- */

export default fx;